Relative Humidity – What Is It And Why Is It Important?

Humidity Control
Industrial Measurements
Life Science

The basics
Put simply, relative humidity (RH) is a measure of the water vapor content of air. More explicitly, it is the amount of water vapor present in air expressed as a percentage (%RH) of the amount needed to achieve saturation at the same temperature.

RH is strongly proportional to temperature and highly sensitive to temperature changes. This means that if you have a stable temperature in your system, your RH will also be stable. As well as temperature, relative humidity also depends on the pressure of the system in question.

Some helpful rules of thumb
There are some helpful rules of thumb to help us understand how RH works at a basic level, though it’s important to remember that unless you’re in a closed system such as an environmental test chamber, other factors can affect results.

The first rule of thumb is that as temperature increases, air becomes drier (RH decreases) and as temperature decreases, air becomes wetter (RH increases). When thinking about pressure, the rule of thumb is that as pressure decreases, air becomes drier (RH decreases) and as pressure increases, air becomes wetter (RH increases).

Why is it important to monitor relative humidity?
By far the biggest reason to monitor relative humidity is to control moisture around a final product. In most cases this means making sure that the RH never rises too high. For example, let’s take a product like chocolate. If the RH in a storage facility rises above a certain level and remains above that level for a sufficiently long period of time, a phenomenon called blooming can occur. This is where moisture forms on the surface of the chocolate, dissolving the sugar. When the moisture evaporates, the sugar forms larger crystals, leading to discoloration.

Humidity can also have a harsh – and expensive – impact on products such as building materials. Say you’re building an extension to your property and you lay a concrete subfloor before putting down hardwood flooring. If the concrete isn’t sufficiently dry before you lay the floor it can cause huge problems because any moisture from the concrete will naturally try to migrate to a drier area – in this case the flooring material. This can cause the floor to swell, blister, or crack – undoing all your hard work and leaving no option except replacement.

Humidity is also a big problem for products with extreme sensitivity to moisture, such as certain pharmaceuticals. This is because it can alter the characteristics of the product until it becomes useless, which is why products like medical pills and dry powders are stored in controlled conditions at precise humidity and temperature levels.

Finally, relative humidity is also an important factor in building automation systems focused on human comfort, such as air conditioning. The ability to measure and control RH not only helps to maintain a comfortable environment inside a building, but it also helps to optimize the efficiency of HVAC systems by providing an indication of how much outside air being taken in needs to be conditioned, depending on the temperature outside.

Want to learn more? Download our Humidity eGuide for Smart Industries to get a handy package with links to a humidity calculator, drying simulation, webinars and other information.


Prakash Kumar

Feb 6, 2019
Please suggest an economical humidity and temperature measuring instrument within your range
Temperature range 0 to 100 degree C
Pressure: o to 500 mmH20

Vaisala Customer Service

Feb 8, 2019
Thanks for your question. The temperature in your application goes up to 100 °C. This limits your options to models with a remote probe. Depending on the expected humidity level, you can find a suitable instrument from following product lines:
0-10 %RH: DMT340-series.
10-100 % RH HMT330-series or Indigo HMP-probes.

Varying pressure in your application has some effect to the humidity reading. To help you decide if it's needed to compensate this effect or not, please take a look at our humidity calculator: .
This tool helps you to demonstrate the effect of different pressures.

carl xynon

Nov 6, 2021
who is the beneficiaries in using the temperature and humidity monitor system?


Nov 24, 2021
Hello Carl, thank you for your question!
It would actually be everyone’s interest that the temperature and humidity monitoring systems are in place in all relevant installation positions starting from manufacturing, covering storing, selling, and shipping all the way to the customer. This way the end product is always of quality, the reseller, and the manufacturer can rest easy knowing what the product is of good quality, the buyer and/or user can trust that the product does not cause harm or delays or require time-consuming reclaiming. Hope this answered your question.

Environmental Test Chamber

Aug 4, 2023
Thank you for shedding light on the revolutionary potential of Environmental Test Chambers in the field of biotechnologies. 'Exploring Cutting-Edge Tools' was a fitting start to the article, introducing readers to this advanced technology. It's exciting to see how precise control and manipulation of conditions are redefining the parameters of scientific research. Looking forward to learning more


Aug 28, 2023
Thank you for your kind and inspiring comment.

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